Industrial systems include a variety of components, including a multitude of sensors and actuators, that are implemented to execute various automated tasks in order to produce a desired product or carry out a specific process. Each individual industrial component is typically controlled, e.g., an actuator is instructed to move a robotic arm in a particular manner, or communicated with, e.g., a sensor value reading is received to adjust a process accordingly.
As shown in FIG. 1A, an industrial system 100 is used to direct individual connections, e.g., via cables 110, to connect a controller, such as a programmable logic controller (PLC) or Programmable Automation Controller (PAC) 115, to each component 120 of the system 100. This is a costly setup and produces many inefficiencies, as it requires a multitude of controllers, even for a single machine having multiple components. The control signal was transmitted using an analog or a digital signal sent over the individual cables 110. While simple in theory, such a setup requires high maintenance, high setup costs, and significant amounts of time spent configuring and setting up each component of the system.
Alternatively, industrial systems, as shown in FIG. 1B, include a mission critical link system 130 with a master gateway (or simply “master”) 140 connected to a controller 115 and configured to communicate with multiple industrial components 160. The master 140 offers a more centralized approach, with a single master 140 connected to many components 160. The connection may be established over direct cable 150 connections. A standardized protocol, such as IO-Link®, is an example implementation of such a system.
A master 140 is configured to connect to multiple devices (e.g., devices that may operate as “slaves” in a master-slave star topology) 150, which may be easily connected to actuators, sensors, and the like. The sensors may include smart sensors providing valuable diagnostic information as well as updated status reports.
However, this setup retains a number of the drawbacks of the older systems, most notably the requirement for physical cables to be run between a controller and each component of the system. The setup of such wiring is expensive, time-consuming and can be significantly limiting in many industrial applications. For example, running cables in a sealed “clean” room used in many industries can be awkward and can compromise the sealed nature of the room. Further, certain mobile systems that require automated vehicles, e.g., robots configured to move stock or equipment around a warehouse, would be heavily encumbered by requiring a physical cable be attached to each vehicle.
In response to these concerns, a mission critical wireless link (MCWL) system, as shown in FIG. 1C, has been developed to implement a mission critical link system over wireless communication, obviating the need for cumbersome wires. The IO-Link® Wireless (IOLW) specification is an example of a mission critical wireless link system and describes a time-division multiplexing (TDM) network configured to communicate with multiple devices. The master downlink is a single broadcast message per a master track (i.e., one message sent for all devices within a track), while the multiple devices and components use a synchronous (i.e., synchronized by an external clock) TDM method for uplink. The master tracks are synchronized and use frequency-division multiplexing (FDM). The master 140 is therefore connected via a wireless link to the various devices 160.
FIGS. 2A and 2B show the uplink packet structure of an exemplary mission critical wireless link connection of a single track 230 within the system. In this example, the mission critical wireless link is an IO-Link Wireless system. The packets are serially sent wirelessly, i.e., one after the other, from various components 220 to the master 140 with a predefined delay between each packet. In the wireless IO-Link standard, such a delay is 8 microseconds (μs) and the gap can be jittered down to 4 μs. The master 140 may be configured to implement frequency hopping to minimize any interference of ambient wireless signals. Per frequency out of the hopping frequencies table, the master 140 is configured to send a downlink message to all devices within the track 230, with up to 8 devices per track. As an example, if the start of the synchronization time of the downlink is marked as T=0 μs, then a first device uses time slot 0, 232, to start its uplink at T0=416+208=624 μs. The next device uses time slot 1, 234, which start at T1=T0+104 μs =728 μs. The period 233 between each packet is 8 μs.
As shown in FIG. 3A, the network configuration of an IO-Link wireless network 300 includes one master 140 with five channels or tracks 315. Each track 315 is connected to a wireless antenna 320 and is configured for TDM between up to eight devices 325. The five tracks 315 run simultaneously using frequency spaced hopping sequences.
FIG. 3B is a graph 350 of the spectrum of the industrial, scientific, and medical (ISM) band running a mission critical wireless link network. The ISM band is a group of radio frequencies (RF) that are internationally designated for use in the industrial, scientific, and medical fields. In one such band, the channels are spaced apart by 1 megahertz (MHz) and include the range from 2400-2480 MHz. Each channel may have one or more wireless transmitters transmitting over that channel. The relative amplitudes, as seen by a receiver for such signals, are affected by the distance between the receiver and the transmitter, the transmitter's transmission power, and any channels placed between the two. The channel may include nulls, where the signal cancels out almost entirely, causing large attenuation on adjacent channels.
As shown in FIG. 3B, it is important to note that a desired signal, e.g., 360, may be significantly less powerful than a neighboring undesired signal, e.g., 370, due to the fact that the transmitter being used may be positioned farther away from the receiver than the undesired transmitter. It should be noted that at a receiving port of the master 140 (i.e., the antenna 320 of a track), each time may have a different receiving power as a function of distance and fading of the channel in use.
FIG. 4 is a diagram of an exemplary implementation of a master 140 on an IO-Link network. Due to the short delay between the packets, each track might require at least two independent transceivers 410 and 420 that toggle between the packets, as the short delay between the packets is typically shorter than the processing time of the transceivers 410 and 420, thus prohibiting a single modem from handling all of the incoming packets efficiently. The delay is typically resolved by employing two independent transceivers per track as shown in FIG. 4. In another configuration, the master 140 includes two radios per track.
Although this option offers full usage of the radio in a sparse TDM network, the implementation of such a master is costly because it requires additional receivers in the transceivers to keep a single receiver at maximum gain and not allow an automatic gain control (AGC) to converge. If an automatic gain control converges, the adjacent channel rejection (i.e., a carrier-to-interference ratio, or C/I performance) is hindered significantly. Another requirement is to have the AGC converge on the first packet and maintain the AGC convergence value for the rest of the packets. This, however, hinders sensitivity to subsequently received signals.
FIG. 5 is an example block diagram of a conventional implementation of a receiver, generally referenced as 500, as part of a master's transceiver operable in an IO-Link Wireless network. In the shown architecture, there are multiple feedback loops, including one from the AGC 510 to the low-noise amplifier (LNA) 525, from the AGC 510 to a voltage gain amplifier (VGA) 530, and another one from the carrier frequency offset (CFO) correction 550 to a rotator. A packet detector correlator 560 issues a reset for all components of the receiver 500 when a packet preamble is detected. All control loops and configurations, such as the AGC gain 510 controlling the LNA 525 and VGA 530, are reset simultaneously when the previous packet reception has ended and the receiver 500 is ready to receive the next packet. The receiver 500 is effectively completely reset to an initial state before a new packet reception begins. An example of such an implementation can be found in many Bluetooth and Wi-Fi receivers.
The implementation of a receiver 500 operating in an IO-Link network master suffers from a major limitation: the synchronous reset of all control loops and state machines prohibits beginning to receive a new packet until the preceding packet has been completely received by all elements of the chain. In this example, a maximum likelihood sequence estimator (MLSE) 535 must clear the entire bit stream before a reset to the entire modem can be issued. Since a guard time between the packets is shorter than the processing time of the entire chain (the antenna to bit stream), a separate receiver is required to receive the next packet. Therefore, at least two independent receivers must be implemented in a master gateway using such a receiver 500 architecture.
In the case of two receivers per track, one receiver would receive the odd numbered packets, while the second would receive the even numbered packets.
FIG. 6 is a diagram of the timing differences between an IO-Link 600 and a BLE 610 implementation. In the IO-Link 600 setup, there is a short time gap 650 between the packets. In the BLE implementation 610, the minimum time gap is 150 μs, while in the IO-Link implementation the minimum gap last 4 μs (under a worst-case jitter and severe fading channel scenario).
Therefore, there is a need for a wireless IO-Link implementation that allows for maximal performance (C/I performance and sensitivity), while only requiring one receiver per track to minimize costs.